Diamond conditioner disks have been used in CMP processes to great effect to maintain the roughness of polyurethane polishing pads. These disks have been produced and marketed by several vendors to standards of reliable quality and effectiveness. Generally, diamond conditioner disks are evaluated based on, among other things, the total number of diamonds present on the surface of the disk and the number of diamonds remaining after certain specified periods of use or environmental testing. However, the effectiveness of the diamond conditioner disk actually depends not upon the total number of diamonds present on the surface of the disk but upon the number of active diamonds present.
Active diamonds are the diamonds that actually contact and abrade the surface of the CMP pad during CMP processing. The diamonds on more topographically prominent areas of the surface of the diamond conditioner disk and, where diamonds are collected together on the surface of the disk, diamonds that are further from the disk surface than others will, from a simple geometric standpoint, be more available to contact a surface such as that of a CMP pad brought into contact with the diamond conditioner disk. The number of active diamonds present in any given situation depends upon the total number of diamonds on the diamond conditioner disk, their grouping, the surface characteristics of the diamond conditioner disk including the topography and the load on the diamond conditioner disk. Although simple microscopic examination of diamond conditioner disk sectors and estimation based on the geometric patterns of initial diamond placement and surface area have long provided a method to determine an approximate total number of diamonds on the surface of a diamond conditioner disk, to date there has been no simple, reliable, cost effective method to measure the number of active diamonds.
If the number of active diamonds on the surface of a diamond conditioner disk could be determined easily, this would allow manufacturers to control and better maintain the quality of the disks in terms of their actual effectiveness in abrading the CMP pad during CMP processing. The surfaces of diamond conditioner disks are not perfectly planar and the grouping of diamonds may vary depending upon the production method and specific topography of the diamond conditioner substrate surface. Additionally, the diamonds may be grouped differently on different disks or on disks made where the diamonds are added by different processes. Although disks may have the same total number of diamonds, because of the aforementioned variations in disk topography and diamond grouping, there may be considerable variation from disk to disk in the number of active diamonds and consequently in how effectively these diamond conditioner disks can abrade the surface of the CMP pad.
To date, no effective counting method has been disclosed and manufacturers and users have had to rely on such essentially ineffective methods as estimating the total number of diamonds present on the conditioner disk surface.
For example, U.S. Pat. No. 7,011,566 describes a method for determining how effectively conditioning of the CMP pad is being conducted. However the method taught by the '566 patent reveals neither the total number of diamonds nor the number of active diamonds on the diamond conditioner substrate.
Similarly, in Bubnick et al., “Effects of Diamond Size and Shape on Polyurethane Pad Conditioning,” Abrasive Technologies, 2004, available at http://www.abrasive-tech.com/pdf/effectsdiamond.pdf, the size and shape of diamonds are taught to be important for the effective life of the diamond conditioner but neither the total number of diamonds nor the number of active diamonds are either determined or considered.
Also in Bubnick et al., “Optimizing Diamond Conditioning Disks for the Tungsten CMP Process,” Abrasive Technologies, 2002, available at http://www.abrasive-tech.com/pdf/tcmptungsten.pdf, the authors teach that manipulation of “diamond concentration” together with other diamond characteristics can be instrumental in lengthening diamond life on diamond conditioners but fail to teach how to determine diamond concentration generally, or active diamond concentration in particular.
Additionally, in Goers et al., “Measurement and Analysis of Diamond Retention in CMP Diamond Pad Conditioners,” 2000, the authors refer to specific alignment and placement of diamonds at the microscopic level on diamond conditioners which would enable one to generally determine the total number of diamonds on the surface of the diamond conditioner disk; however, the number of active diamonds cannot be calculated or estimated from the total number of diamonds alone. The difference in the number of active diamonds to total surface diamonds is at least two to three orders of magnitude. Goers et al. does not provide either a description of active diamonds, a discussion of their importance or a means of determining how many active diamonds are present.
In Dyer & Schlueter, “Characterizing CMP pad conditioning using diamond abrasives”, the authors refer to determining “diamond loss” by microscopic examination of diamonds on the surface of the diamond conditioner disk. In addition to diamonds placed individually on a predetermined grid on the diamond conditioner surface, diamonds arranged in clusters of 1-9 from which an estimate of total diamond number could be made are given but, again, no reference is made to the existence or determination of the number of active diamonds.
In Zimmer & Stubbmann, “Key factors influencing performance consistency of CMP pad conditioners,” available at http://www.diamonex.com/diabond_key_factors.htm, the authors discuss the concept of “working grit density”, which is defined as “the total amount of grit in contact with the pad divided by the total area of the conditioner.” The authors teach that working grit density can be measured “by inspecting the conditioner after usage and counting the number of grit particles which show physical wear compared to the total number of grit particles within a given area. The ratio of the two densities can then be used as a figure of merit for the quality of the conditioner.” Similarly in Thear & Kimock, “Improving productivity through optimization of the CMP conditioning process,” available at http://www.morganadvancedceramics.com/articles/cmp_optimization.htm, the authors define “working grit density” as “the number of grit particles that show physical wear compared to the total number of grit particles within a given area. This calculation is made by inspecting the conditioner after use and is used to indicate the quality of the conditioner.” However, the post-usage visual inspection procedures taught by these references can only be used effectively on a worn disk and provide no direct information on the active diamond count at various stages of life. In addition, it is difficult to distinguish between diamonds that wear because they are cutting the pad and those that wear because they make contact but do not cut.
Users of diamond conditioner disks need to know that they are receiving the same quality of product from diamond conditioner disk manufacturers from the standpoint of process effectiveness on a consistent basis and such a test would allow users to better determine specifications for what they require. Users may also want to know how well their disks are faring under certain operating conditions and an accurate method of determining active diamonds on the diamond conditioner disk will provide them with useful information in that regard. Finally, from a research and development standpoint, the results of such a test would provide makers of diamond conditioner disks with more useful information about how to improve existing manufacturing processes for diamond conditioner disks or in the development of new CMP and related processes.
The present invention seeks to provide an accurate and consistent method for determining the number of active diamonds on a conditioner disk. These and other advantages of the invention will be apparent from the description of the invention provided herein.